(a) Field of Invention
The present disclosure of invention relates to liquid crystal displays, and particularly to a contact sensing liquid crystal display panels.
(b) Description of Related Technology
Liquid crystal displays (LCDs) are now widely used as one form of flat panel displays. A liquid crystal display conventionally has two spaced apart substrates, on one of which field generating electrodes such as pixel electrodes are disposed and on the other of which a common electrode is formed. A liquid crystal material layer is interposed between the two substrates. In the liquid crystal display, voltages are applied to the field generating electrodes so as to generate an electric field extending through the liquid crystal material layer. Alignment of liquid crystal molecules in the liquid crystal material layer is controlled by the electric field. In one class of embodiments, the polarization of incident light or backlight is controlled by the alignment of the LC molecules and thus a desired image is formed on the display.
A touch sensitive screen panel is a device that is structured for allowing an associated machine such as a digital computer to perform touch-indicated commands such as the writing of a character, the drawing of a picture, or the executing of an icon in response to touching at a corresponding spot by a user's finger or by a touch pen (or stylus) brought into engagement with a screen surface. In one class of embodiments, the liquid crystal display to which the touch screen panel is attached is used to determine whether a user finger or a touch pen or another surface engaging means touches the screen surface and to determine the touch position information thereof. The cost of the liquid crystal display, however, increases due to mounting of a separate touch screen panel. Because of additional processes for adhering the touch screen panel to the liquid crystal panel, the yield of liquid crystal displays is reduced, the luminance and the viewing angle of the liquid crystal panel are deteriorated, and the overall thickness of the product increases.
In order to overcome such problems, a variety of technologies for integrally embedding sensors in the liquid crystal display have been developed so as to avoid adhering a separate and discrete touch screen panel to the LCD panel. The integrated sensors should be able to determine whether contact is made by a user's finger, and to determine the contact location by for example sensing light variation or pressure variation made by engagement of the user's finger.
In one method of sensing variation of pressure applied to the screen by the user's finger, contact information is obtained through determination of a capacitance variation between two terminals due to corresponding variation of a distance between the two terminals. The applied contact force should be in a range wherein the two terminals of the variable capacitor do not contact each other. If the two terminals are shorted, it is difficult to obtain correct contact information through this method. Thus, according to convention, a relatively large distance between the two terminals must be sufficiently maintained. However, in this case, a cell gap of the liquid crystal display is disadvantageously increased.
On the other hand, the liquid crystal display portion of an integrated touch and display system includes a thin film transistor (TFT) and the thin film transistor includes a semiconductive active layer. However, in the process for manufacturing the thin film transistor, it is not easy to obtain uniform semiconductor characteristics in the semiconductive active layer of the display device. That is, in one type of design, if the characteristics of the thin film transistor are changed, the detection signal of the sensor may also be changed according to its position in the display device relative to varied TFT's. As a result, an error of determination of degree and/or position of contact may be generated.
The above information disclosed in this Background section is only for enhancement of understanding of the technology background of the invention and therefore it may contain information that does not form part of prior art that heretofore is already known to persons of ordinary skill in the art of integrated touch and display systems.